Tractor load weighing device

ABSTRACT

A device for monitoring a load in a container ( 16 ) being towed or carried by a tractor or other vehicle. The device comprises a top link ( 30 ) connecting a part ( 28 ) of the container to a tool frame ( 26 ) or the like of a tractor or other towing vehicle. The tension in the link is dependent on the weight of the load in the container, and a load cell ( 36 ) comprising an array of strain gauges is provided to measure the tension in the link and provide an indication of the tension at a position remote from the link, for example in a tractor cab.

This invention relates to a device for use with a tractor-carriedcontainer which enables the container load to be monitored.

Seed drilling and fertilizer spreading is often carried out using ahopper attached to the rear of a tractor on a cantilevered frame.Support for the hopper is typically provided by a lower beam, which canbe raised and lowered by a hydraulic mechanism on the tractor and aboutwhich the hopper is pivotable, and a top link in the form of aload-bearing turnbuckle which is under tension and which can be used toadjust the angular position of the hopper.

In seed drilling or fertilizer spreading, it is important to spread theseed or fertilizer in the correct amount per unit area. For example, themost usual method of drilling is to allocate a weighed trailer load ofseed to the area to be drilled on the basis of the intended seed rate inKg/hectare. The drill manufacturer's calibration routine may have beencarried out on a proportion of the seed outlets in preparation. The seedis transferred in the field from the trailer to the drill hopper bymeans of an auger and sowing begins. The hopper is replenishedas-necessary and a tally is kept of the number of refills. Checking thenumber of refills against the hectare meter of the tractor gives someindication of seed rate, but it is difficult to estimate how much seedis left in a partly full hopper so that the true seed rate can only bedetermined when the trailer is empty. This process generallynecessitates adjustments to the seed flow from time to time so thatalthough the overall intended seed rate may be achieved the distributionmay be uneven. There is therefore a need for a weighing mechanism whichwill give an indication of the amount of seed or other material left inthe hopper at any given time.

DE-A-3714642 describes an agricultural spreader carried on a tractortool frame by a three-point lifting device. A top link of the liftingdevice, which is under tension, incorporates a weighing device tomonitor the weight of the load in the spreader and the rate ofspreading. A problem which arises with the use of such a tension link asa weighing device is that the measured weight may vary according to theangular orientation of the link. In particular, the weight distributionover a three-lifting device may vary according to whether the tractor ison level ground or on a slope.

EP-A-407705 discloses a three-point lifting device for a tractor-mountedhopper in which the weight of the hopper is measured by sensors at eachof the three load-bearing points of the device. The angular orientationof the device is also sensed and a signal is fed to a microprocessortogether with signals from each of the three weight-sensors.

EP-A-537857 and EP-A-797082 also disclose lifting devices incorporatinga strain gauge or other weight sensor and an angle measuring cellarranged to correct measured weight values to compensate for the angularposition of the tractor and container.

The present invention provides a device for monitoring a load in acontainer being towed or carried by a tractor or other vehicle, thedevice comprising one or more strain gauges to provide a signalindicative of the load at a position remote from the device and a levelindicator adapted to give a signal indicative of the angular orientationof the device relative to the horizontal, characterised in that thestrain gauge or gauges and the level indicator are incorporated togetherin a tension link securable to the container as part of a towing orsupport mechanism therefor, such that the tension in the link isdependent on the weight of the load in the container, the signalprovided by the strain gauge being indicative of the tension in the linkand the level indicator being mounted in the tension link so as to berotatable relative thereto about a horizontal axis, to set anorientation for calibration of the device.

The device of the invention is preferably in the form of a top linkextending between a tractor and the container, for example a hopperwhich is pivotally mounted on a cantilevered frame. The link ispreferably in the form of a turnbuckle so that the angular position ofthe container can be adjusted.

The link preferably includes a load cell, comprising an array of straingauges, arranged to provide an indication of the tension in the link, tobe displayed in a cab of the towing or carrying vehicle. The display canbe calibrated with the container both empty and filled with a knownquantity of specified material such as particular seed or fertilizer,with the same orientation of the device as shown by the level indicator,so that the tension reading gives an indication of how much remains inthe container at any given time. The tension data can also be used, withthe aid of a suitable microprocessor, to provide an indication of therate at which material is being distributed from the container, bylinking the measured load in the container, and its rate of depletion,with the speed of the vehicle and the area being swept by it.

A rough reading can be displayed continuously, with more accuratereadings being taken from time to time by stopping on relatively levelground and using the lifting device to set the tension link at thepredetermined orientation at which calibration took place.

A preferred embodiment of the invention will now described withreference to the accompanying drawings wherein:

FIG. 1 is a schematic side elevation of a tractor and seed drillcombination incorporating a weighing device in accordance with theinvention;

FIG. 2 is an enlarged partial view of the top link and tension gauge ofthe device of FIG. 1;

FIG. 3 is a schematic circuit diagram for the device; and

FIG. 4 shows schematically an arrangement of switches for the levelindicator.

Referring first to FIG. 1, a tractor generally indicated by 10, having acab 12, carries a seed drill 14 in the form of a hopper 16 supported ona cantilevered frame 18 comprising a pair of substantially L-shapedframe members, one on each side of the hopper, pivoted at coaxial pivotpoints 19 to a pair of parallel levers 20 which in turn are pivotallyattached at pivot points 21 to a rigid tool frame 26 mounted at the rearof the tractor. A pair of operating levers 24, arranged to be raised andlowered by the tractor motor, are connected to the levers 20 byconnecting rods 22 to raise and lower the levers 20 and hence also raiseand lower the seed drill 14.

A top link 30 connects a higher part 28 of the hopper frame to the toolframe 26. It is this top link which incorporates a load cell, comprisingan array of strain gauges, forming part of a weighing device inaccordance with the invention, as will be described in more detail withreference to FIG. 2.

Referring now to FIG. 2, the tension link 30 comprises a pair ofthreaded rods 31, 32, pivotally connected respectively at 28 to thehopper frame and 26 to the tool frame of the tractor. The tension bar ispositioned centrally, midway between the rear wheels of the tractor,with the link rods 22 of the two lever systems positioned on each sideof it.

The respective threaded portions of the rods 31, 32 are connected by aturnbuckle 347 which can be used to adjust the overall length of thetension bar and hence the angular position of the hopper.

Because the centre of gravity of the hopper is located well behind thepivot 19, the hopper has a tendency to swing backwards and downwardsaway from the tractor. It is prevented from doing so by the tension link30, which is accordingly under permanent tension. The magnitude of thistension will of course depend on the total weight of the hopper and itscontents, and thus can be used to give an indication of what weight ofmaterial is in the hopper.

The turnbuckle 34 is associated with a load cell 36 arranged to measurethe tension in the link and to feed a tension reading to amicroprocessor and digital display as will be discussed below.

Because emptying of the hopper will cause a shift in its centre ofgravity, the tension measured by the load cell may not be directlyproportional to the weight of material in the hopper. Nonetheless, therelationship will be sufficiently close to a linear one to give a usefulreading with the display calibrated with full and empty readings. Themicroprocessor can in any case be programmed to compensate for a degreeof non-linearity.

FIG. 3 shows schematically the circuitry used to give an in-cab displayof the hopper contents.

As can seen in FIG. 3, the load cell 36 effectively comprises a variableresistor, the resistance of which varies according to the tension in thetop link 30. The power supply to the load cell is provided by thetractor battery 40, and the resistance in the load cell is measured by amicroprocessor 42. This in turn sends a signal to a digital display 44located in the tractor cab.

Raising and lowering the hopper will swing the top link through smallangle. The load cell incorporates a level indicator 46 which feeds tothe microprocessor a signal indicative of the angular orientation of theload cell, and hence of the hopper, which can affect the reading givenby the load cell which will accordingly require correction.

The level indicator includes a rotatable knob 45 which is used to setthe orientation at which calibration is to take place. The in-cabdisplay 44 also includes a set of indicator lights or light-emittingdiodes 50, with upper and lower red lights 51, 53 and a central greenlight 52. When the device is at the desired orientation, only the greenlight shows. When the device moves through a predetermined minimum anglefrom this orientation, one or other of the red lights shows.

As shown in FIG. 4, the level indicator 46 comprises a pair of mercuryswitches 63 and 64, mounted within the device so as to be rotatabletogether with the knob 45 while remaining in fixed orientations relativeto one another. The two mercury switches have an angle X between them ofa few degrees, typically 2 to 5°. Each of the switches 63, 64 has oneterminal connected to a point A of an indicator circuit. Switch 64 hasits other terminal connected to point B of the indicator circuit, andswitch 63 has its other terminal connected to a point C of the samecircuit. Connecting A to B will illuminate one red light and connectingA to C will illuminate the other red light. If neither connection ismade, the green light shows, indicating that the device is level.

In the horizontal position shown in FIG. 4, both switches are open sothat only the green light will show, indicating that the unit is at thecorrect level for calibration. If the unit is rotated slightly clockwiseas shown in FIG. 4, switch 63 will close, connecting A and C, while 64remains open. If the unit is rotated a few degrees anti-clockwise,switch 63 will open again while switch 64 closes, connecting B to A.

A corrected reading of the measured resistance in the load cell willgive an indication to the driver in the cab of the contents of thehopper. The microprocessor 42 may however also use data from thetractor's hectare meter 48, which indicates the area being swept by thetractor, to give a continuous or intermittent reading of the rate atwhich seed in being distributed, in units of weight per unit area,usually Kg/hectare. The driver can then adjust the feed rate of thehopper, to ensure at an early stage that the correct amount of seed isbeing distributed.

The mode of operation of the described system is suitably as follows:

1. Place the tractor on a level surface.

2. Raise the hopper to the desired weighing height, which in the case ofa fertilizer spreader will be the operational height.

3. Adjust the level indicator 46 so that only the green light 52 shows.

4. Calibrate the system by recording and entering the hopper weight whenempty and when filled with a load of known weight of product.

5. Start spreading or drilling checking the weight in the hopper at anytime by raising the spreader to the desired weighing height, at whichonly the green indicator light shows.

There is thus provided a load monitoring system which enables thecorrect distribution of seed, fertilizer etc. from an early stage in theoperation rather than by trial and error.

What is claimed is:
 1. A device for monitoring a load in a containerbeing towed or carried by a tractor or other vehicle, the devicecomprising at least one strain gauge to provide a signal indicative ofthe load at a position remote from the device and a level indicatoradapted to give a signal indicative of the angular orientation of thedevice relative to the horizontal, wherein said at least one straingauge and said level indicator are incorporated together in a tensionlink securable as a single unit to the container as part of a supportmechanism for the container, such that the tension in said single unitlink is dependent on the weight of the load in the container, the signalprovided by said strain gauge being indicative of the tension in saidsingle-unit tension link and said level indicator being mounted in saidsingle-unit tension link so as to be rotatable relative thereto about ahorizontal axis, to set an orientation for calibration of the device. 2.A device according to claim 1 wherein the link is in the form of aturnbuckle.
 3. A device according to claim 1 wherein the link includes aload cell comprising an array of strain gauges, arranged to provide anindication of the tension in the link.
 4. A device according to claim 1wherein the level indicator comprises a plurality of mercury switches infixed positions relative to one another but rotatable together as a unitabout a horizontal axis, different combinations being open or closedaccording to the angular orientation of the unit.
 5. An assemblycomprising a device according to claim 1 mounted as a top link extendingbetween a tractor and container, the container being pivotally mountedon a cantilevered frame.
 6. An assembly according to claim 5 wherein thecontainer comprises a hopper arranged to deposit the load at acontrolled rate.
 7. An assembly according to claim 5 wherein saidindication of tension in the link is provided in a cab of the tractor.8. A method of monitoring the controlled distribution of bulk materialfrom the container of an assembly according to claim 5, which comprisesthe steps of calibrating a display, indicative of the tension in thelink with the container both empty and filled with a known quantity ofsaid bulk material and the tension link at the same orientation in eachcase, and thereafter using tension readings from said display as anindication of how much of said material remains in the container at anygiven time.